The present invention relates to a binocular.
Conventionally, a binocular includes two (left and right) telescope systems, a focus adjustment mechanism for focusing the telescope systems, and a diopter correction mechanism for adjusting a diopter of the telescope systems. In general, the focus adjustment mechanism is constructed to move two lens groups which respectively belong to two telescope systems of the binocular, while the diopter adjustment mechanism is constructed to move a lens group which belongs to one of the telescope systems (for example, the right telescope system). The binocular is provided with a focus adjustment knob for operating the focus adjustment mechanism and a diopter correction knob for operating the diopter correction mechanism.
In case where the lens group moved by the diopter adjustment mechanism belongs to the right telescope system, the diopter correction process includes the following two stages. In a first stage, an observer observes an object with left eye (through the left telescope system) and operates the focus adjustment knob thereby to focus the left telescope system on the object. In a second stage, the observer observes the same object with right eye (through the right telescope system) and operates the diopter correction knob thereby to focus the right telescope system on the object.
However, since the observer must close right eye in the first stage and close left eye in the second stage, the diopter correction process is troublesome. Further, when the observer closes one eye, it may affect the diopter characteristics of the other eye, which lowers the accuracy in the diopter correction. Although it is alternatively possible to put an external cover on the binocular to shield one of the telescope systems, it also makes the diopter correction process troublesome.
Furthermore, if the observer mistakenly operates the focus adjustment knob in the second stage, it may change the focus of left telescope system which has been set in the first stage. In this case, it is necessary to repeat the first stage.